The present invention relates in general to systems for producing cryogenic gases, and more particularly, to a system for converting liquid cryogen into a high pressurized gas and for storing and dispensing the resulting pressurized cryogenic gas.
Cryogenic gases are used in a variety of industrial and medical applications. Such cryogens are typically stored as liquids in vessels, however, because one volume of liquid produces many volumes of gas (600-900 volumes of gas per one volume of liquid) when the liquid is permitted to vaporize/boil and warm to ambient temperature. To store an equivalent amount of gas requires that the gas be stored at very high pressure. This would require heavier and larger tanks and expensive pumps or compressors.
Many industrial applications require that the cryogen be supplied as a high pressure gas, such as in the range of 350 psig to 450 psig. For example, high pressure nitrogen and argon gases are required for laser welding while high pressure nitrogen, oxygen and argon gases are required for laser cutting. In addition, in some industries, it is desirable for a system to provide both liquid cryogen as well as high pressure cryogenic gas.
It is known to use compressors or pumps to pressurize cryogenic gases or liquids, respectively. In the latter case, the pressurized liquid may be directed to a vaporizer that uses ambient heat to provide cryogenic gas at high pressure. Such approaches, however, suffer from the disadvantages associated with using a compressor or pump. These disadvantages include high initial and replacement costs and service or maintenance requirements.
Alternatively, prior art cryogenic gas delivery systems that direct cryogenic liquid from a bulk tank into a smaller tank for pressurizing, so that the pressurized liquid may be forced to a vaporizer to produce vaporized gas, are known. Such systems are illustrated in U.S. Pat. No. 2,040,059 to Mesinger, U.S. Pat. No. 4,175,395 to Prost et al. and U.S. Pat. No. 5,924,291 to Weiler et al. As illustrated by the Mesinger ""059 patent and the Weiler ""291 patent, it is also known to build the pressure in the smaller pressure building tank by use of a pressure building circuit that receives liquid from the tank, vaporizes it using ambient heat via a vaporizer and returns the resulting gas to the head space of the tank. In contrast, the Prost et al. ""395 patent builds the pressure within the smaller tank by the transfer of ambient heat through the smaller pressure building tank wall.
While these systems are effective, the system of the Weiler et al. ""291 is somewhat complex. In addition, the systems of the Mesinger ""059 and the Prost et al. ""395 patents are limited in the gas pressure levels that may be obtained and provided. Also, none of the systems provide both gas and liquid and none feature a modular construction for ease of retrofitting existing cryogenic liquid dispensing systems.
Accordingly, it is an object of the present invention to provide a system that builds the pressure of a liquid cryogen to convert the liquid cryogen to a cryogenic gas at a high pressure.
It is another object of the invention to provide a system that increases the pressure of the liquid cryogen by using ambient heat.
It is another object of the invention to provide a system that dispenses both liquid cryogen and high pressure cryogen gas.
It is another object of the invention to provide a system for pressurizing the cryogenic liquid and converting it into high pressure cryogen gas that is modular so that existing liquid dispensing systems may be retrofitted with the gas generating module.
It is still another object of the invention to provide a system that builds the pressure of a liquid or gas cryogen without pumps or compressors.
The invention is a system for converting a liquid cryogen into a high pressure cryogenic gas. The system includes a storage vessel or tank full of liquid cryogen that is in communication with a feed line. The feed line is in communication with a pressure pod. Liquid cryogen is transferred from the storage vessel via the feed line to the pressure pod. Cryogenic liquid in the pressure pod is warmed and vaporized by ambient heat so as to increase the pressure therein. Once the pressure in the insulated tank reaches a first predetermined level, a regulator valve opens allowing the liquid cryogen to travel to a heat exchanger. The heat exchanger receives the liquid cryogen and vaporizes it. The resulting vapor is directed back to the pressure pod thereby further increasing the pressure of the liquid cryogen therein. Once the pressure in the insulated tank reaches a second predetermined level that is higher than that of the first predetermined level, a dispense valve opens.
Once the dispense valve opens, the pressurized liquid cryogen is directed to a vaporizer. The vaporizer converts the liquid cryogen into a cryogenic gas for dispensing and storage. Alternatively, the dispense valve may be set to open when all of the liquid cryogen in the pressure pod has been converted to cryogenic gas which may then be dispensed or stored.